Mammographic imaging is well established as the primary screening modality for breast cancer. A suspicious finding on a mammographic examination may lead to imaging with another modality to further investigate the suspicious finding and ultimately to a biopsy being performed to confirm that cancer is or is not present. The other modalities may include a diagnostic mammogram, an ultrasound (US) examination, a magnetic resonance imaging (MRI) procedure, or a nuclear medicine procedure (known as scintimammography). Depending on the nature of the finding and the imaging system with which it was found, the surgeon or radiologist may be guided in the removal of tissue for pathological examination by one of these imaging systems. Breast biopsy systems have been produced and marketed which rely on x-ray guidance, US guidance, and MRI guidance.
Mammograms are x-rays that image tissue densities, not cancer activity. It can be difficult to identify cancerous lesions using mammography, especially when patients have dense breast tissue, multiple suspicious lesions or clusters of microcalcifications, palpable lesions not detected by mammography or ultrasound, post-surgical or post-therapeutic mass, implants, or have been taking Hormone Replacement Therapy.
MRI has shown usefulness as a next-step imaging modality for difficult-to-diagnose cases. Much like x-ray mammography, breast MRI relies on anatomical or structural information, but provides much more detailed images. It is limited, however, by its highly variable specificity, which can range from below 37% to 97%. Combined with its high sensitivity, it is expensive, may require multiple days to complete, and produces a high false positive rate.
Ultrasound is also commonly utilized as a next-step after a questionable mammogram and is good at determining if a suspect mass is solid or fluid-filled. However, ultrasound demonstrates a low specificity rate that can produce misleading results and indicate biopsy where one may not be needed.
Although biopsy systems employing x-ray, ultrasound, and MRI modalities exist, there remains a need for achieving further accuracy in determining the location of potentially cancerous lesions and for the accurate guidance of biopsy systems to the cancerous lesions.